Chemical, jump, and tracer diffusion coefficients D, Dj and D*, respectively, were determined by Monte Carlo simulations on a square lattice for the case of nearest-neighbor attractive interactions. D was determined by the fluctuation autocorrelation method and by the Kubo-Green equation, using values of <(δN)2>/<N> determined from isotherms. <(δN)2>/<N> could only be determined above Tc and, for this situation, the two methods yield identical D values within the error of the simulations. Distinct high- and low-T regimes for D were observed, because of the changes in <(δN)2>/<N> with T, with much higher activation energies and pre-factors for T/Tc < 1.4 than for T/Tc > 1.4. For D* and Dj much smaller effects were seen. The numerical values of activation energies suggest that diffusing atoms were either isolated atoms in the dilute lattice gas or those which became detached from corners of close-packed (1x1) islands below Tc, but had a higher nearest-neighbor complement in the dense lattice gas above Tc.

A Monte Carlo Study of Surface Diffusion Coefficients in the Presence of Adsorbate-Adsorbate Interactions. II. Attractive Interactions. C.Uebing, R.Gomer: The Journal of Chemical Physics, 1991, 95[10], 7636-40